The present invention relates to low cost integrated circuit oscillator sources and more particularly to a recessed diode in a metal coaxial cavity coupled to image line or microstrip waveguide oscillator sources for use in millimeter-wave integrated circuits.
Radar and communications circuits, as well as other high performance circuits, require oscillator sources which are able to operate at high frequencies. Particularly, the present invention deals with oscillators in the 60-70 Ghz frequency range. Ideally, an oscillator should possess a high "Q" and thus "see" a low impedance and also be capable of providing an output signal of significant power levels in response to an input signal of a predetermined magnitude.
In known manner, extremely high frequency (EHF) oscillators, for operation in the millimeter-wave range, may be obtained by means of a coaxial cavity which is made to resonate by means of a diode which is capable of producing a frequency component of a desired frequency. The dimensions and shape of the cavity define a resonant structure in which a sustained oscillation at one frequency is established. The actual frequency of oscillation is related to the size and shape of the cavity and is described by convention by the so-called 1/2.lambda. value of the cavity. The prior art shows coaxial cavities in metal structures. They include auxiliary metal-walled circuits for guiding the energy from the cavity to other circuits. Metal-walled structures, however, increase the cost of an oscillator because additional precision machining inside a structural assembly is required. Furthermore, oscillator cavities fabricated primarily in metal are less compatible with dielectric line and/or microstrip circuits and additional means are therefore required for coupling the oscillator to other elements of a circuit. Additionally, metal based oscillators are more expensive, are of greater weight and size thus limiting their applications.
A further limiting factor is that at progressively higher frequencies, skin effect losses in metal-walled structures rise because skin effect losses are proportional to the square root of frequency.